1. Field of the Invention
The present invention relates to a thermal activation device which heats a heat-sensitive adhesive sheet to activate an adhesive layer thereof, and to a technique for stably discharging the activated heat-sensitive adhesive sheet.
2. Description of the Related Art
A heat-sensitive adhesive label is anticipated for use as a label pasted on a product produced/marketed in a food factory or a supermarket for indicating, for example, a trade name, a price, a use-by date, and the like. The heat-sensitive adhesive label has an adhesive layer which does not have an adhesive force in a normal state. This adhesive layer is activated by application of heat energy to this adhesive layer, making it possible to paste it on an object. Moreover, on an upper surface side of the heat-sensitive adhesive label, a printing surface which develops color when heated is formed. Including such a heat-sensitive adhesive label, a sheet having a similar adhesive layer is generically referred to as a heat-sensitive adhesive sheet in this specification.
Patent Document 1-- JP2001-48139
Patent Document 2-- JP2003-316265
Here before, as a thermal activation device which activates such a heat-sensitive adhesive sheet, a “label issuing device” described in Patent Document 1 and the like have been proposed.
Moreover, as described in Patent Document 2, a thermal activation device has also been proposed, which uses a thermal head composed of heat generating elements formed on a planer substrate surface in a width direction thereof, and a platen roller brought into press-contact with this thermal head, and which is adapted to activate the adhesive layer of the heat-sensitive adhesive sheet by sandwiching the adhesive sheet between the thermal head and the platen roller and heating the adhesive sheet.
However, the conventional device described above does not have a structure which forcibly separates the heat-sensitive adhesive sheet from between the thermal head and the platen roller after the heat-sensitive adhesive sheet is thermally activated, and accordingly, the trailing end portion of the heat-sensitive adhesive sheet discharged from a discharge port is in contact with the thermal head. Then, when such a state continues for a predetermined period of time, the following problems occur. That is, residual heat remaining in the thermal head may be transferred to the trailing end portion of the heat-sensitive adhesive sheet, resulting in the printing surface of the portion developing color, and the adhesive layer may be solidified, resulting in sticking of the heat-sensitive adhesive sheet to the head.
In this connection, the inventors of the present invention examined the following mechanism as the structure which forcibly separates, from the thermal head, a heat-sensitive adhesive sheet that has been thermally activated. Specifically, in the mechanism, a conveyor roller that is rotationally driven is situated rearward of the thermal head and the platen roller, and a space large enough for the heat-sensitive adhesive sheet to pass therethrough is provided above this conveyor roller (see a discharge roller 56 and a discharge guide 57 in FIG. 1)
In such a way, the heat-sensitive adhesive sheet is conveyed with its one side supported, and thus the contact pressure of the heat-sensitive adhesive sheet and the conveyor roller becomes the minimum. Thus, the above mechanism advantageously reduces the occurrence of such a problem in which a part of the adhesive layer of the heat-sensitive adhesive sheet is adhered to the conveyor roller. Moreover, the interval above the conveyor roller can be set relatively large, and accordingly, the above mechanism also has an advantage in that, even if an adhesive material adheres to the conveyor roller and then accumulates, the mechanism is less prone to such a problem in which the path of the heat-sensitive adhesive sheet is blocked owing to accumulation of this adhesive material.
However, it has been found that, with the construction in which the conveyor roller that conveys the heat-sensitive adhesive sheet while supporting one side thereof is situated rearward of the thermal head and the platen roller in such a way, a problem occurs once in a while in which the heat-sensitive adhesive sheet slides on the conveyor roller and the trailing end portion of the heat-sensitive adhesive sheet cannot be separated from the thermal head.
An object of the present invention is to provide a thermal activation device including a discharge mechanism which forcibly separates, from a thermal head, an adhesive sheet that has been thermally activated and conveys the adhesive sheet, the thermal activation device realizing discharge of the adhesive sheet in a stable state while minimizing adhesion of an adhesive material to the discharge mechanism and the influence of such adhesion.